1. Field of the Invention
This invention relates to a device for controlling the travel of a gearbox selector fork and for activating the positive clutch of a sliding gear when synchronized with the selected gear ratio.
This device may be used to electronically control the synchronization of the shifting of the gearbox to shift gears "on-the-fly" without any synchronizing ring.
2. Description of the Prior Art
Traditionally, the synchronization of the rotational speed of two gears before they mesh is provided by mechanical friction members known as synchronizers. Generally, the mechanical synchronizers, which include friction rings, have a number of disadvantages, particularly in terms of efficiency and size. Furthermore, they significantly increase the mechanical complexity of the gearbox construction.
The present invention eliminates the above disadvantages by offering a device which synchronizes the pairs of gears, upon shifting thereof, using fully electronic means.
French Patent No. 2,417,689 and its first continuation 2,431,642 disclose a mechanism consisting of a quick clutch release to effect the disengagement of the gear followed by a new clutching after the neutral position has been obtained. Thereafter, the engine speed and, therefore, that of the clutched gear, is monitored to bring the gear to the desired synchronization speed. Once this result is obtained, both transmission shafts of the gearbox are positively clutched.
In fact, considering both the timing and the swiftness of the operation, it appears that the accuracy of the gearshift operation depends on three main parameters.
The first parameter, .alpha., is the ratio between the gearbox input angular speed and the gearbox output angular speed.
The second parameter, .mu., is the .alpha. variation speed during the synchronization phase, namely the speed of convergence toward synchronization during the synchronization phase.
The third parameter, T, is the time required for the actuator to engage the positive clutch after receiving the order.
Considering the above, if .alpha..sub.C is the value of ratio .alpha. to which the positive clutching order is given so as to perform the operation, and .alpha..sub.m is the gear ratio to be clutched, the following observations can be made. .alpha. is known, but not accurately; .mu. cannot be exactly calculated and varies throughout the synchronization phase; and T does not remain constant from one operation to another.
In conclusion, the error that can be made depends on the three values .alpha., .mu., and T. It appears that the positive clutching accuracy upon synchronization could be improved by reducing T.
In particular, if the duration T became shorter than the calculation intervals of .alpha. and .mu., namely A T, the process would be made easier due to the fact that the positive clutching order has to be sent shortly before the synchronization is obtained.